Vibration or impact indicator



Nov. 25, 1952 LAN OR, R 2,619,605

VIBRATION OR IMPACT INDICATOR Original Filed Jan. 10, 19 14 A MPL F If Rosc/uoscons INVENTOR doaz fl 6 lA/vcoAzz/xz :s ATTORNEY.

Patented Nov. 25, 1952 VIBRATION Y OR IMPACT INDICATOR Joseph H:ljancor; Jr., Silver Spring, Md., assignor' to" Tli'e SperryCorporation, a corporation of Delaware Original application. January 10,1944, Serial .No.

517,657.. Divided and this application Decemher 3, ,1949",-Serial No.130,979

4 Claims; I

My invention relates to vibration pick-up devices in generaland' theiruse'in vibration detecting systems, and concerns itself primarily withvibration pick-up devices especially adapted to detect detonation incombustion engines, or other sudden, high frequency; impacts; Thisapplication'is adivisionof my prior-application for VibrationPicli-upDeviceand Systems, now Patent No; 2,534,276, December 19, 1950, andconstitutes an improvement of thedetonation detector of the type shownin my jointpatent'with C. S. Draper, No- 2,275,675, forDetonation'DetectorSystems, dated Marc-h 2; 1942. This' type-of detector isexternallymounted on thecylinder wall of an engine asdistinctfrom-the'prior'type; such as" shown in" the patent te Draper, No;2,202,900, datedfiune 4, 1940*fOrTndicating Apparatu's, Which'requi'resa hole in' the cylinder wall so that the pressure'ofthe gases within'thecylinder was 'transmitted directly to a diaphragm forming'a part of thedetonation detector. The system of my joint patent withDraper-marked agreat advance over" the priortype requiring a hole in the cylinder wall;since it was found that the vibrations impartedtothe cylinder wallby'detonation were sufiicient'to detect detonation and-violent impactsof that nature in a better manner than the prior type-in which thedirect effect oftheexplosionin' the cylinder on the diaphragm was mixedwith the'resulting vibration of the cylinder 'wallsandattached housingof the detonation detector;

According to my present invention, 1' further simplify and improve thelater'type of'detonation detector: by confihing'the signal produced to asingle phenomenomnamely; thevariations of the magnetic linesoiforcein'the coilby variation' in the magnetostrictive effect on a rod placedunder stress against the cylinder wall. In the aforesaid priorDraper-and Lancor device, thevariations in a magnetic gap were causedby: detonation due to' the difference in periodic frequency between the1 diaphragm con-- nected ata'spaced point or points to the cylinderwall. and a-magnetic pick-upy coil and" core, but other effectsof thehigh frequency detonation suchv asv that due to magnetostr-ictiveeffects in the metal core cause the results to be somewhat uncertainan'd'non-un'iform';

According to my present invention,: l endeavor to confinethe efiectoithe vibrations due; to detonation to the magnetostri'ctiveeffect upona magnetostrictive member placed under: initial stress ortensioni and 1tightly secured to: a-.cylinderrwall'. No" airigap-is therefore:emp'loyed iand 2, when detonation occurs the stress in themagnetostrictive element is rapidly changed due to the resultingvibrations, said changes effecting achange in the number ofmagneticlines threading the coilsurrounding the magnetostrictive elementthereby producing an E. M. F. generally' proportional to and in phasewith the vibrations of the vibrating member.

Asan object of myinvention, I wish to provide a'vibration pick-up devicein which changes in'the physical characteristics of a'vibratory massvary the number'of magnetielines threading. a coilto induce thereinelectromotive forces "which are proportional to higher order derivativesof the vibrations occurringin a vibratorymember, i; e-;, the rateofchange of vibratory accelerations.

It is also an object oi." my invention to provide a magnetostrictivevibration pick-up device which may be used in connection with adetonation or other impact or shock detecting system and which isadaptable for external mounting on the apparatus in'which the detonationor shock is to be detected.

It is an object of 'my invention toprovide a vibration pick-up deviceinwhich a wire coil is associated with a permanent'magnet" whose linesof force form a magnetic circuit which interlinks said" coil and inwhich is interposed a magnetostrictive element arranged to be responsiveto the vibrations of a vibrating member. Moreover, the magnetostrictiveelement is selected to have anatural frequency of vibration higher inorder than the frequencies of vibrations to which it is responsive, andis operable to alter the number of magnetic lines threading said coilinaccordance' with changes in the permeability'of the element due tostresses-set up by external vibrations.

Yetanother object of' my invention is to provide a detonation'system'inwhich a magnetostrictiv'e pick-up device is arrangedfor externalmounting on a cylinder or the metal part subject to an impac-t'in whichdetonation is to be detected and which is associated with a cylinderselector switching means, a variable timing means, an amplifying device,and a visual indicating means; in'such' manner that the phenomena'ofdetonation may be observed and indicated as occurring in'individualcylinders or in a plurality of cylinders and which may be isolated fromother vibration patterns set up in the cylinderwalls due to valveaction, etc., as shown in my aforesaid parent application.

By my invention, Iprovi'de an engine analyzer in whichvibrationsindicative-of conditions capable of causing engine failuresand of maladjustments may be detected in their incipient state by meansof a magnetostrictive vibration pick-up element permanently ortemporarily mounted on the engine's cylinder walls and elsewhere, andassociated with a selector switching device and variable timing means insuch a manner that electromotive forces generated in the pick-up devicesmay be selectively passed to a visual indicating means in which the wavepatterns characteristic of maladjustments occurring within the enginemay be observed and analyzed.

In carrying out my invention, I provide a permanent magnet in the formof a ring or hollow cylinder which is contained in or forms a suitablehousing for the entire unit. Within the magnet is a rod or stud formedof material exhibiting pronounced magnetostrictive properties andlocated within the field of the magnet. The

stud is preferably placed under tension to clamp the magnet undercompression and there is usually secured to the stud a mass increasingits inertia. The unit is securely fixed to the cylinder wall or toWhatever device is being tested so that when detonation or other highfrequency oscillations occur, high frequency stresses are set up in themagnetostrictive device thereby changing the number of magnetic linespassing therethrough. This action induces an electromotive force in apick-up coil around the rod and thus interlinked by these magnetic linesof force, which alternates at a frequency equal to the frequency ofvibrations of the vibrating member and with an amplitude which is afunction of both the frequency and amplitude of said vibrations.Suitable electrical connections and wiring lead the potentials generatedin the coil to any suitable form of indicator, such as an oscilloscopeor neon lamp. v

The single figure shows a vertical section of one of my improveddetonation detectors with diagrammatic connections to an indicator.

My detonation indicator is shown as made up of a rod 45, which ispreferably of magnetostrictive material, such as an alloy high in nickelcontent, and is shown threaded at each end. One end 57 of the rod 45 isscrewed and staked into the top plate or cover 43 of the device, theother end 46 threaded into bottom plate 58 forming the base of the unit.A coil of fine wire 54 is wound around the non-magnetic ring spacer 5|which is clampedv between the top plate 48 and the coil retainer 49staked to the rod at 52 and which adds to the inertia of the rod 45. Apermanent magnet 55 which is cylindrical in shape is placed around thecoil assembly and is held tightly clamped, that is, under compression,between the top plate i8 and the base 56. Said base has extendingtherefrom a threaded stud 51 adapted to be threaded into a tapped holel3 extending part way into vibratory member I 3 to which the pickupdevice may be attached. If such member is a cylinder wall of an engine,the hole l3 should not extend through the wall.

The sensitivity of my device may be adjusted by varying the amount oftension imposed upon the rod 45 in as'emblying the device. Terminalconnections 59 and B! are provided for receiving electromotive forcesinduced in the coil 55 and the ends of the latter are connectedtherewith by conductors, such as 62, which are insulated from the topplate Q8 by insulators G3 and 64.

My detonation detector may be connected to any suitable form ofindicator, such as an oscilloscope N31; or neon lamp Hit or both througha suitable amplifier I05, the connections 59 and SI being connected toinput terminals I92 and I03 on the latter. As explained in my aforesaidparent application, if the device is used for detecting detonation in acombustion engine, selective switches may be interposed between thepick-up unit and indicator for the purpose of confining the indicationsto the period of the cycle when detonation occurs and also for studyingthe behavior of any one of a plurality of cylinders of a multi-cylinderengine.

In operation my pick-up device is screwed into and therefore vibrateswith the cylinder wall or other metallic member under test. Since thevibration produced by the phenomenon of detonation is usually on theorder of approximately 10 cycles per second and 10* inches in amplitude,it is possible for my pick-up device to discriminate between vibrationsof considerably larger amplitudes and lower frequencies. The mass of therod 45 together with that of the parts clamped to it 49 and El, are soselected that it has a natural frequency of vibration in excess of thefrequencies produced by detonation within the cylinder wall. Because ofthis fact, the pick-up device operates, in a sense, as an accelerometerand electromotive forces are induced in the coil winding 54 which areproportional to higher order derivatives including at least the thirdderivative of the vibrations set up by detonation.

As will be apparent to those skilledin the art, it is, of course,possible to provide a system, such as that described, with filtercircuits which will render the system inoperative to pick up the largeamplitude, low frequency vibrations that interfere with the study ofdetonation. Such precaution is not necessary, however, in a systemprovided with my pick-up, since the mass and dimensions of themagnetostrictive element may be so chosen as to make it responsive onlyto higher order derivatives of the vibrations detected. Theelectromotive forces generated in each of the pick-up devices areproduced by a change in the number of magnetic lines threading the coiland its magnetostrictive core 45, which emanated from the magnet 55.This change is produced by the stresses set up in this element by thevariations in stress resulting from the vibration of the cylinder walland transmitted through the stud mounted base of the pick-up device. Dueto the change in the number of lines interlinking the coil,electromotive forces are induced in the latter and are transmittedthrough the connections 59, M provided on the pick-up and thence throughsuitable leads to terminals I02, I03 on the amplifier 1M. Preferably,the field strength of the magnet 55 should be maintained at a level suchthat the magnetostrictive rod 45 will not become saturated.

In aircraft applications, where the detection of detonation is ofconsiderable importance, it is often not feasible to burden the pilotwith the duty of observing on the screen of an oscilloscope the variousvibration patterns, nor is it feasible in some installation to encumberthe plane with the added weight of an oscilloscope. In these cases, anindicator such as that illustrated as the neon tube I 06 may beprovided'on the panelboard of the plane and the amplifier I9 3 adjustedto the proper gain so that the tube Will be fired only by, and to givean indication of the presence of detonation.

- As many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madeWithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a vibration pick-up device adapted to be rigidly mounted on asurface comprising a housing including a rigid base and cover, a wirecoil, a magnetostrictive rod rigidly held under tension between saidbase and cover, a hollow cylindrical magnet surrounding said rod andcoil and clamped under compression between said base and cover by thetension of said rod, said rod extending through said winding, stud meansrigidly attaching said base of said housing to said surface wherebyvibrations in said cylinder will induce an electromotive force in thecoil surroundmg said magnetostrictive element as a result of thevariation in magnetic characteristics of said element.

2. A device for detecting detonation in a cylinder of an internalcombustion engine, comprising a housing adapted to be directly andrigidly attached to the outer wall of said cylinder, a magnetostrictiverod like weighted element secured at each end in said housing so as toplace the rod under tension and thereby hold the housing together, saidrod normally vibrating at a frequency approximating the detonationfrequency characteristics of said engine, means for impressing amagnetic flux upon said element, and a winding linking said flux, soconstructed and arranged that vibrations in the magnetic fluxconductivity of said element due to vibrations set up by detonation insaid cylinder Will induce correspondingly varying electromotive forcesin said winding.

3. A pickup or detector for indicating shocks to a body, comprising arigid base adapted to be directly and rigidly connected to said body, ahollow cylindrical permanent magnet, a closure at each end thereof, ofpermeable material, a rod of magnetostrictive material threaded at eachend into said closures so that when said rod is placed under tension,said cylindrical magnet is held under compression between said closures,and a pick-up coil surrounding said rod, in which a signal is inducedupon shock by the variation in the magnetic flux threading said coil dueto the magnetostrictive properties of said rod, said signal beingadapted to actuate a vibration indicator.

4. A device for detecting detonation in a cornbustion engine cylindercomprising a rigid base adapted to be directly and rigidly connected tothe outer wall of said cylinder, a sleeve of paramagnetic material onsaid base, a cap closing the outer end of said sleeve and a rod ofmagnetostrictive material threaded at its ends into said base and capand serving to clamp the aforesaid parts together by being placed undertension, said rod having a substantial mass intermediate its ends, amagnetic circuit including said sleeve as a flux producin means and saidrod, a winding surrounding a portion of said rod, the flux in saidcircuit varying with stresses due to forced vibrations in said rodcaused by detonation in said engine cylinder to induce varyingelectromotive forces in said winding.

JOSEPH H. LANCOR, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,616,416 Fessenden Feb. 1, 19271,882,401 Pierce Oct. 11, 1932 2,396,540 Stansfield Mar. 12, 19462,435,031 Burns et a1 Jan. 27, 1948 2,445,318 Eldredge et a1 July 20,1948 2,472,127 Slason June 7, 1949

